Apologies if this is a known bug, I looked through the issues on here and on Github but didn’t find anything. If you’d like, I can create a bug report on Github.
I’m seeing a bug where a ground-clamped billboard is initially displaying at the wrong position in 2D and Columbus modes. Panning or zooming usually will cause the billboard to “jump” to the correct spot. Luckily, this is easily reproduced on Sandcastle.
Steps to reproduce:
Visit the Ground Clamping example: https://cesiumjs.org/Cesium/Apps/Sandcastle/index.html?src=Ground%20Clamping.html&label=Showcases
Switch to either 2D or CV - Note: switching from 3D to 2D will sometimes correct the position at the end of the transition.
Notice the billboard displaying at the wrong position.
It looks like the bug was originally introduced in 1.23.0, 1.22.2 does not exhibit this behavior. I’ve been able to reproduce this in both Chrome 56.0.2924.87 and Firefox 51.0.1. Let me know if you need more information.